Applicant proposed previously in JP-A-10-204499 a sheet type laundry detergent involving no scatter nor leakage of a detergent composition, which has a thin layer of a doughy detergent composition whose penetration hardness is in a specific range and a water-soluble support of sheet form disposed on both sides of the thin layer.
Unlike powdered detergent, the sheet type laundry detergent is advantageous in that detergent does not scatter when put into a washing machine and is easy to handle.
Since the doughy detergent composition is not always highly flowable, it is necessary to form the doughy detergent composition into a thin film with uniform thickness and width which exhibits high solubility when used. Further, it is not easy to form the thin film without developing defects such as air bubbles.
If the field of soaps such as sheet type soaps, a production method using a blade coater was proposed in JP-B-51-44524. The method disclosed, however, aims to obtain uniform and flexible sheet type soap by heat-melting a coating layer followed by cooling for solidification and differs from the present invention in technical means and object.
JP-A-53-91913 proposes a method of obtaining a sheet type laundry detergent in which a slurry is applied and, after drying, stripped off. Without specifying conditions for carrying out the application and the like, the method is practically difficult to carry out applying the doughy detergent composition dealt with in the present invention.
A doughy detergent composition is a viscous mixture made of a flowable material, such as liquid surface active agents, in which a powdered composition, such as solid detergent particles, is dispersed in high concentration. It exhibits complicated flow behavior, having properties intermediate between wet powder and a slurry. It is noted that the doughy detergent composition changes its properties from fluid-like to powder-like with time after preparation. The change in properties becomes more conspicuous with an increase of powdered composition concentration in the doughy detergent composition. In forming a thin layer out of a doughy detergent composition with such properties, it is preferred that the doughy detergent composition has high flowability, and for that purpose it is preferred for the composition to have a low concentration of solid detergent particles. On the other hand, a higher concentration of the solid detergent particles is preferred for developing sufficient detergent performance. Thus the flowability and the detergency of a doughy detergent composition are conflicting each other.
To use an application means in forming a thin layer of a doughy detergent composition is described in JP-A-10-72599, col. 9, ll. 14–17 and JP-A-10-204499, col. 14, ll. 10–13, but the publications do not mention conditions and the like for carrying out the application on an industrial scale, for example, for mass production; for such matter does not directly concern the inventions of the publications.
Apart from this, JP-A-5-189744 specifies the viscosity of a thixotropic fluid by setting the hysteresis loop area of a torque curve obtained with a viscometer at or below a specific value. The purpose of specifying is to control the surface roughness of an applied magnetic layer. The technique is different from the present invention of which the object is to increase the flowability of a doughy composition having a high concentration solid detergent powder to ensure satisfactory coating properties while retaining high detergency and solubility.
JP-A-7-209512 discloses an adhesive paste for a color filter which has a yield value of 0.1 Pa or higher and a non-Newtonian viscosity index of 0.9 or smaller. In this invention attention is paid to the intercept of a viscosity-shear rate curve, with no reference to the properties intermediate between fluid-like and powder-like as represented by the overall slope of the viscosity-shear rate curve.